This invention relates in general to golf balls and, more particularly, to a golf ball having a cover material exhibiting improved playability characteristics and resilience and performance properties.
The assembly of a golf ball generally involves molding a cover around a solid or wound core. Golf balls with wound cores are typically referred to as "three piece" balls because they consist of three basic components: (1) a solid or liquid-filled center; (2) rubber winding around the center, and (3) the cover. Similarly, solid cores are referred to as having a "two piece" construction, since they consist solely of a solid core and a cover. A third type of ball, known as a "one-piece" ball is also known in the art. As the name suggests, one piece balls are solid balls of homogeneous construction made by any conventional molding method suitable for the purpose.
The composition of the golf ball cover has proven to be a factor in overall golf ball performance. Historically, three piece and two piece golf balls had covers made of Balata, a natural resin obtained from trees in South and Central America and is essentially made up of transpolyisoprene. Balata is readily adaptable to molding processes to produce a high quality golf ball.
Balata is still used today as a cover material because of the "click" and "feel" provided by the balata cover to the golfer. "Click" is the sound made by a golf club head when it hits the ball. "Feel" is the overall sensation transmitted to the golfer after hitting the ball. Balata covered golf balls are also used because of the excellent playability and good flight performance qualities. These balls give good flight distance and skilled golfers can impart desirable spin to the ball, enabling it to draw or fade in flight. Also, especially with high-lofted clubs, the backspin allows the ball to stop abruptly on approach shots.
However, balata type materials are expensive and the manufacturing procedures required are time-consuming, labor-intensive and therefore expensive.
The majority of modern golf balls use a two piece construction with covers made of a durable synthetic thermoplastic resin such as Surlyn, a product of E. I. DuPont de Nemours Company, Incorporated. Synthetic thermoplastic cover materials have been used with limited success. They are durable and produce satisfactory flight distance. Additionally, they are less costly to manufacture than balata covers. However, these materials are hard and therefore lack the "click" and "feel" of a balata ball. Moreover, it is not possible to impart to such balls the desirable spin characteristics required by skilled golfers. It is desirable, however, to utilize a synthetic cover material for improved process manufacturing and to increase durability and resilience performance.
In an attempt to overcome the negative factors of the hard ionomer covers, low modulus SURLYN ionomer-covered golf balls were introduced in the early 1980's. These SURLYN ionomers have a flexural modulus of from 25 to about 40 as measured on she Shore D scale-ASTM 2240. E. I. DuPont De Nemours & Company has disclosed that the low modulus ionomers can be blended with other grades of previously commercialized ionomers of high flexural modulus of from about 30,000 to 55,000 psi to produce balata-like properties in a golf ball covered with this material. The qualities found in these golf balls, especially as to durability, were not optimal.
U.S. Pat. No. 4,884,814 to Sullivan teaches blending a hard ionomer resin with a soft ionomer resin to produce a cover having enhanced playability characteristics and a good durability for continuous play. In that reference, a golf ball cover blend includes a hard Surlyn ionomer resin, having a hardness of 60-66 on the Shore D scale as measured in accordance with ASTM method D-2240, and various soft Surlyn ionomer resins having hardness ranging from 25-40 on the Shore D scale. Specifically, the patent claims 25-70% of the hard ionomer which is a sodium or zinc salt of the specified copolymer and having flexural modulus of 30,000 -50,000 psi, blended with 75-25% of the soft ionomer which is a sodium or zinc salt of a specified terpolymer and having a flexural modulus of 3000-7000 psi.
U.S. Pat. No. 5,120,791, also to Sullivan, is designated an improvement to the earlier patent and reveals a composition said to have enhanced carrying distance. The blends of this second Sullivan patent include 90-10% of an acrylic acid based hard ionomer neutralized with sodium or zinc and having a Shore D hardness greater than 50 and a flexural modulus up to 70,000 psi, with an acrylic acid based soft ionomer having a Shore D hardness of 20-40 and a flexural modulus of 2000 to 8000 psi.
Covers produced according to these references have improved playability over traditional Surlyn covers but at a cost of losing resilience and distance properties.
Accordingly, it is an object of the present invention to provide a golf ball having a synthetic cover material.
Another object of the present invention is to provide an improved synthetic cover material for a golf ball.
It is another object of the present invention to provide a golf ball having a synthetic cover material that achieves the click, feel, playability and flight performance qualities of Balata covered golf balls.
A further object of the present invention is to provide a golf ball having a cover material that has improved process manufacturing as well as durability and resilience.